PALYNOLOGY AND PALEOECOLOGY OF LIGNITES FROM THE MANNING FORMATION (JACKSON GROUP) OUTCROP IN THE LAKE SOMERVILLE SPILLWAY OF EAST-CENTRAL TEXAS

Four palynomorph assemblages, whose parent plants contributed to the f ormation of the lignite, occur in the lignite seams and associated sed iments from the Manning Formation (Jackson Group) outcrop in the Lake Somerville spillway of Texas. The Cicatricosisporites-Laevigatosporite s fern assemblage occurs in the middle and upper seam and probably der ived from a freshwater herbaceous mire community. The Momipites corylo ides-Arecipites columellus-Liliacidites assemblage occurs in all three seams and probably derived from a freshwater mire forest with an open canopy or shrub community. The Momipites coryloides-Nyssa-Rhoipites a ngustus assemblage occurs in the lower and middle seams and probably d erived from a different freshwater mire forest. The Cupuliferoipolleni tes-Cupuliferoidaepollenites liblarensis-Siltaria cf. S. scabriextima assemblage occurs at the top of the lower and middle seams, which are overlain by marine sediments. The association between Cupuliferoipolle nites dominance and the presence of marine diatoms and brackish or mar ine trace fossils in the lignite suggests that this assemblage may hav e derived from a mangrove (i.e. marine or brackish) mire forest. Howev er, other factors may influence its distribution. Ailanthipites berryi , possibly derived from a tree or shrub related to the 'tree of heaven ', predominates in the claystone underlying the lower lignite seam and may have colonized the coastal plain prior to the initiation of peat accumulation. We can differentiate lignite samples dominated by fern s pores, Momipites pollen and Cupuliferoipollenites pollen based on gas chromatography-mass spectrometry (GC-MS) fragmentograms of triterpanes (m/z 191) and steranes (m/z 217), The lignite layers dominated by eac h palynomorph assemblage appear to have distinct sources and different early diagenetic (pre-coalification) histories. (C) 1997 Elsevier Sci ence B.V.